Article

# Double Resonant Raman Scattering in Graphite

Institut fur Festkorperphysik, Technische Universitat Berlin, Hardenbergstrasse 36, 10623 Berlin, Germany.
(Impact Factor: 7.51). 01/2001; 85(24):5214-7. DOI: 10.1103/PhysRevLett.85.5214
Source: PubMed

ABSTRACT

We find that the electronic dispersion in graphite gives rise to double resonant Raman scattering for excitation energies up to 5 eV. As we show, the curious excitation-energy dependence of the graphite $D$ mode is due to this double resonant process resolving a long-standing problem in the literature and invalidating recent attempts to explain this phenomenon. Our calculation for the $D$-mode frequency shift ( $60{\mathrm{cm}}^{\ensuremath{-}1}/\mathrm{eV}$) agrees well with the experimental value.

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• "The laser beam with 0.5 mW power was focused on a spot of about 1 μm in diameter on the studied surfaces, the spectral resolution being 0.5 cm or better.@BULLET G band (~1582 cm ) is the only first-order Raman band in graphene, it is ascribed to optical (iTO and LO) doubly degenerate phonons of E —symmetry at the Γ point (Tuinstra and Koenig 1970); @BULLET D band (~1330 cm ) is due to breathing-like modes of C hexagonal rings (corresponding to transverse optical phonons near the K point) and requires a defect for its activation via an intervalley double-resonance Raman process (Thomsen and Reich ( 2000 )); @BULLET D′ (at about 1612 cm ): similar to the D-band, which occurs via an intravalley double-resonance process in the presence of defects (Ferrari ( 2007 )); @BULLET D″ band (at about 1145 cm ) resulting from double-resonant intervalley scattering of LA phonons on defects (Herziger et al. 2014). The intensity of this band should be about 100 times lower than those of D mode. "
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• "The first-order D peak cannot be visible in pristine graphene because of crystal symmetries[42]. For the D peak to occur, a charge carrier has to be excited and inelastically scattered by a phonon, and then a second elastic scattering by a defect or zone boundary must occur to result in recombination[43]. The presence of disorder in sp 2 -hybridized carbon systems results in resonance Raman spectra, and thus makes Raman spectroscopy one of the most sensitive techniques to characterize disorder in sp 2 carbon materials.For the GO samples that were electrochemically reduced within 15 V, two other modes exist at 2680 cm −1 (2D-mode) and 2947 cm −1 (D+G-mode). "
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• "I D /I G ratio was used to evaluate the average size of sp 2 domain and the degree of disorder and in present case the same is 0.14 which indicates high order and low degree of structural defects as a result of efficient deoxygenation of carboxyl , epoxy and other oxygen functional groups. The position, shape and full width half maximum (FWHM) of the second-order 2D band are sensitive to the number of layers in grapheme nanoplatelets (Ni et al. 2007; Ferrari and Robertson 2000; Ni et al. 2008), which may be triggered by double-resonant effect, in other words, may be caused by changes in electronic and vibrational properties (Thomson and Reich 2000) XPS scan was adopted to confirm remnant amount of oxygen functional groups that may impair the conductive network and electrochemically active surfaces for supercapacitor applications. The survey scan plotted in Fig. 8a shows C 1 s peak at about 284.78 eV and weak O 1 s peak at about 533.3 eV, which indicates lower oxygen content and the same has been confirmed by Fig. 8b and c. "
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